The present invention relates to ink jet printing devices, and more particularly, to systems for cleaning the orifice plates of ink jet print heads.
It is essential to the proper operation of an ink jet printing apparatus that the orifices of the ink jet print head remain free from dried deposits of ink which may tend to clog the orifices and impair the operation of the print head. As a result, many types of devices have been devised to eliminate collections of dried ink from the orifices of an ink jet print head. Some of these devices employ ink solvents and provide means for flushing the orifices and orifice plate with such a solvent to dissolve these deposits of ink.
For example, in the Yamazaki et al. U.S. Pat. No. 4,296,418, an ink jet printing apparatus is disclosed in which an ink clog is removed from a nozzle orifice by causing solvent to flow through the print head. Solvent is caused to flow through a cap, which is placed over the nozzle of the printer, through the orifices of the nozzle, and to a solvent receptacle upstream of the print head. After a predetermined period of time, the cap is removed from the nozzle and the printing operation is resumed.
The Bader et al. U.S. Pat. No. 4,343,013 discloses a nozzle plate for an ink jet print head which is made of glass and provides an inner surface which is wettable by an aqueous ink. The outer surface of the nozzle plate is coated with a non-wetting material, such as plastic, to prevent deposits of ink at the front surface and around the orifices formed in the plate.
It is believed that a disadvantage with such systems is that it is difficult to clean the outer surface of the nozzle plate with an appropriate solvent since that outer surface is made of a non-wettable material which would cause the solvent to bead rather than form a thin film which would cover the surface and dissolve any ink deposits. Furthermore, in order to clean the orifices formed in such a nozzle plate, it is necessary to provide structure to which either conveys solvent to the interior of the ink jet print head so that it flowed outwardly through the orifices, or, as in the Yamazaki et al. device, collects solvent passing through the orifices at a location upstream of the print head.
The patents to Graf, U.S. Pat. Nos. 4,356,500 and 4,283,730 disclose ink jet printers which provide means for minimizing the accumulation of ink on catchers, a problem which may be considered analogous to minimizing ink accumulation on orifice plates and nozzles of print heads. Both of those patents disclose ink jet printers in which the catcher and orifice plate are enclosed in a gas chamber which promotes the evaporation of ink from those components. The catcher is made of a hydrophobic material such as carbon, polyethylene, polypropylene, or Teflon, to prevent accumulation of dried ink. As with orifice plates, the use of a hydrophobic material to form the catcher may increase the difficulty in efficiently flushing the catcher with a solvent to remove any dried deposits of ink.
Accordingly, there is a need for an ink jet printer which is designed to facilitate the removal of dried ink deposits from the outer surface of the orifice plate. Furthermore, such an orifice plate cleaning system should be relatively simple in construction and not require conduits and connections for flushing a solvent through the print head.